1. Technical Field
The present invention relates to semiconductor fabrication and more particularly to a structure and methods for forming multiple doping regions for finFETs without a critical mask step or structure.
2. Description of the Related Art
Fin field effect transistors (finFETs) have been extensively investigated as one of the future device options for continued scaling of complementary metal oxide semiconductor (CMOS) technology. Most CMOS applications require various types of devices on the same chip. For example, a microprocessor chip usually includes both n-type and p-type (nFETs and pFETs) devices with various threshold voltages (Vt), e.g., high Vt, regular Vt, and low Vt. FinFETs with different Vt require different doping in the fin portions.
Prior art approaches for forming finFETs with different fin doping are complex and costly because they require multiple critical lithography steps for forming fins and masking some fins while doping other fins. Generally, these methods require masking one portion of a semiconductor wafer, performing a doping technique or other process, removing the mask, forming a new mask on another portion of the wafer followed by performing a different doping technique or other process and removing the new mask. The masking and doping processes have to be performed accurately to ensure proper operation of the devices. This incurs considerable time and cost.